A computerized measure of behavioral function with known validity as a measure of brain behavior function, which can be used.in epidemiologic investigations of occupational and environmental exposures, has yet to be identified. The Neurobehavioral Evaluation System (NES) is a battery of computer-assisted behavioral tests developed for such epidemiologic settings. The sensitivity of some subtests of the NES to known neurotoxins has been shown in a number of studies; i.e., subjects with acute experimental or chronic occupational exposure to known neurotoxins show impaired performance relative to controls on certain NES subtests. However, it is difficult to interpret the meaning of these findings, because the brain-behavior relationships which may exist for the NES subtests have not yet been identified. Impaired performance on specific NES subtests or groups of subtests may not reflect cerebral damage at all: It may be due to peripheral sensory loss. If it does reflect cerebral dysfunction, it may do so because of damage to any of several parts of the brain. This lack of specificity regarding brain-behavior relationships is not true of many other behavioral tests used in occupational settings. Several of the tests included in the WHO/NIOSH core test battery , (Johnson, 1987) for example, have been used extensively in populations of patients with known brain damage and the neurobehavioral/neuropsychological meaning of these tests have been well described (Lezak, 1983; Grant and Adams, 1986). In order to begin to develop a similar level of knowledge concerning the cerebral correlates of impaired performance on the NES subtests, the battery will be validated on 3 groups of neurological patients and 2 control groups. This will allow us to determine the sensitivity of each NES subtest to known neuropathology, to determine if there are patterns of performance on the NES subtests which predict known neurologic disorders, and, ultimately, to validate the NES as a measure of CNS function. If the NES is shown to be a valid predictor of specific types of neuropathology, it will greatly enhance the battery's theoretical utility in epidemiologic studies of behavioral neurotoxicology and will provide a new clinical tool for the evaluation of patients with possible brain damage secondary to neurotoxic exposure.